AERO NOMICA ACTA

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I N S T I T U T D ' A E R O N O M I E S P A T I A L E D E B E L G I Q U E 3 - A v e n u e C i r c u l a i r e

B • 1 1 8 0 B R U X E L L E S

A E R O N O M I C A A C T A

A - N° 2 8 8 - 1 9 8 4

Ozone and temperature trends due to the injection of t r a c e species in the atmosphere

by

Guy BRASSEUR

B E L G I S C H I N S T I T U U T V O O R R U I M T E - A E R 0 N O M I E

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F O R E W O R D

T h i s paper has been presented at a seminar organized by the Commission of the European Communities (Climate Program). It will be published in the proceedings of the meeting.

A V A N T - P R O P O S

Cette note a été présentée a un séminaire organisé .le 18 mai 1984 par la Commission des Communautés Européennes (Programme Climatique). Elle sera publiée dans les compte-rendus de la réunion.

V O O R W O O R D

Deze tekst werd voorgesteld tijdens een werkvergadering die op 18 mei 1984 georganiseerd werd door de Commissie van de Europese Gemeenschappen (Klimaatprogramma). Hij zal gepubliceerd worden in de verslagen van de bijeenkomst.

V O R W O R T

Dieser Text wurde präsentiert während der T a g u n g

organisiert am 18 Mai 1984 von der Kommission der Europäische Gemein-

schafte (Klimaprogramm). Er wird publiziert werden in die Rapporten

der T a g u n g .

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OZONE AND TEMPERATURE TRENDS DUE TO THE INJECTION OF TRACE SPECIES IN THE ATMOSPHERE

by

Guy BRASSEUR

Abstract

The paper presents a model of the possible future ozone and temperature changes in relation with the injection in the atmosphere of several trace species produced by man-made activity.

Résumé

Cette note présente les résultats d'un modèle qui prédit les

changements de la quantité d'ozone et de la température sous l'effet de

l'injection dans l'atmosphère de gaz produits par l'activité humaine.

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Samenvatting

Deze tekst geeft de resultaten van een model dat de veranderingen in de temperatuur alsook in de hoeveelheid ozon voorziet onder invloed van de injectie in de atmosfeer van verscheidene gassen die door menselijke activiteiten geproduceerd worden.

Zusammenfassung

Dieser Text gibt die Resultaten eines Modelles das die Veränderungen in der Temperatur wie auch in der Quantität Ozon vorausseht unter dem Einfluss von der Injektion in der Atmosphäre von verschiedenen Gasen produziert von menschlichen Aktivitäten.

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I. INTRODUCTION

Much attention is presently given to the potential effects of gases which are released by the i n d u s t r y and penetrate in the s t r a t o - sphere where they interact with ozone. Among these gases, chlorofluoro- carbons ( C F C ) , methane ( C H

4

) , nitrous oxide ( N

2

0 ) and carbon dioxide ( C 0

2

) play an important role. T h e i r radiative and chemical effects are c u r r e n t l y studied by means of coupled chemical/radiative models (Wuebbles, 1983; Brasseur and De R u d d e r , 1984; B r ü h l and C r u t z e n , 1984, e t c . . . ) which take into account a large number of chemical and photochemical reactions and consider the effect of optically active molecules on emission and absorption processes.

The purpose of this s t u d y is to present and discuss data obtained with such a model, considering plausible scenarios f o r the emission of the optically and chemically active constituents. The time dependent simulation refers to a p r e i n d u s t r i a l atmosphere ( y e a r 1850) and predicts the effects of these gases until year 2080.

The model described elsewhere (Brasseur et al, 1982;

Brasseur and De Rudder, 1984) includes a detailed chemical and photo- chemical scheme, t a k i n g into account the action of o x y g e n , h y d r o g e n , n i t r o g e n , chlorine and carbon species. The vertical temperature profile is derived from a thermal scheme in which the heating is calculated using the parameterization suggested by Schoeberl and Strobel (1978).

The radiative t r a n s f e r in the i n f r a r e d is treated by determining the

transmission function in 4 large spectral i n t e r v a l s . The upward and

downward i n f r a r e d f l u x as well as the corresponding cooling rates are

obtained by solving the radiative t r a n s f e r equation in which the

transmission functions are parameterized as a function of the amount of

absorbing gases. This parameterization is based on a s t u d y made with a

multispectral radiative model by Morcrette ( p r i v a t e communication). An

energy balance is achieved at the top of the atmosphere assuming a

global earth-atmosphere albedo of 0.3. The model extends from 0 to

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70 km. The vertical transport of the trace species and of the heat (especially in the troposphere where convective instability appears) is parametrized by means of an eddy diffusion coefficient.

II. ADOPTED SCENARIO FOR THE MODEL C A L C U L A T I O N

A prognostic of the future state of the atmosphere requires the introduction in the model of a realistic scenario. Because of the large uncertainties in the projected emissions of the pollutants, the following scenario should be considered as an example based on realistic considerations. Figure 1 shows the historical data and the projected values which have been used for the industrial sources of the several halocarbons which are released in the atmosphere (Logan et al., 1978).

The corresponding CIX mixing ratio at the stratopause from year 1950 to year 2080 is reproduced in figure 2. It reaches 9 ppbv in year 2080, that is a factor of 3 larger than the present value.

The C 0

2

amount in the atmosphere during the next century is not straightforward to predict but a number of scenarios for the related emission, based on the projected fossil fuel usage have been developed (Niehaus, 1976; Rotty, 1977 e t c . . . ) . We have assumed for the pre- industrial atmosphere (1850) a mixing ratio of 270 ppmv and, after year 1979 a growth given by (Wuebbles et al, 1983)

f(C0

2

) = 335.0 exp [0.0056 (t - 1979)]

where f ( C 0

2

) is the C 0

2

mixing ratio expressed in ppmv and t the year under consideration.

s

Atmospheric measurements carried out in the last decade have shown a systematic increase in the N

2

0 concentration of about 0.25 percent per year (see e.g. Weiss, 1981; Khalil and Rasmussen, 1981;

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1 0

10 6 _

o <D

fc 10s

a

U) c

if)

< L

y 104

LU cr

cr o

£

10

io

2

3 _

1940 1960 1980 2000 2020 2040 2060 TIME (years)

Fig. 1.- Historical release and assumed future emission of

different halocarbons adopted as a scenario for

the perturbation calculations, after Logan et al.,

1978.

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I

< x >

I

1850 1950 1983 2000

TIME (years) 2020 2040 2060 2080

Fig. 2.- Variation of the CI mixing ratio in the upper stratosphere induced by the halocarbons refease adopted in the scenario and described above

(see fig. 1).

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1983). Such a growth has been assumed to remain constant in the future until year 2080. The N

2

0 mixing ratio in year 1850 is assumed to be equal to 285 ppbv. The value in 2080 is 425 ppbv.

The existence of a systematic trend in the methane amount is subject to discussion. Analyzing a series of measurements made in the past decade and taking into account several corrections made for older data, Ehhalt (1983) does not derive any significant change in the CH^

mixing ratio. However, continuous observations made in the recent years by Rasmussen and Khalil (1981), Blake et al. (1982) and Rowland (1983) show an increase of 1 to 2 percent per year. A value of 1 ppmv has been adopted for the preindustrial mixing ratio with a increase of the order of 1.5 percent/yr for the future, leading to a mixing ratio of 7.5 ppmv in year 2080. The perturbations of CH^, I ^ O and CC^ used as input for the model are given as a function of time in figure 3.

Aircraft emissions have been introduced after year 1950 and are similar to that introduced by Wuebbles et al. (1983). These numbers (see fig. 4) are based on the analysis by Bauer, 1978 and Oliver et a}., 1977. The corresponding trend between 1950 and 2000 may be somewhat overestimated due to the flight reductions in relation with the economic crisis and the increase in the fuel costs. This particular scenario should therefore correspond to an upper limit in the possible ozone change. After year 2000, the aircraft emission is supposed to remain constant. The key parameter in this type of calculation is the ratio between artificial and natural NO sources. The value of this

X

parameter as a function of time is highly uncertain. The adopted sources may lead to an overestimation of the ozone increase in the troposphere.

III. R E S U L T S AND DISCUSSION

The changes which are calculated and discussed below use, as

a reference, the preindustrial atmosphere of year 1850. The variations

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1850 1900 1950 1983 2000 2020 2040 2060 2080 T I M E (years)

Fig. 3.- Assumed evolution of the No0> CC^ and CE^ mixing ratio from the pre- industrial era to year 208CT. These curves, correspond to an increase in N~0 of 0.3% per year from the present day, of 0.56%/yr for CCL and of

1.5%/yr for CH,.

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to I

AIRCRAFT PRODUCTION RATE (cm*

Fig. 4.- Assumed present and future release due to aircraft operations. Curve 1

corresponds to the present day situation and is derived from the

analysis by Bauer (1978). The projected emission for year 2000 shown by

curve 2 is similar to the emission suggested by Oliver et al. (1977)

for year 1990. A linear trend is assuned before 2000. After this

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in total ozone and temperature at the Earth's surface for the scenario described above are listed in the table 1.

This table clearly indicates that the surface temperature increases regularly due essentially to the enhancement of CC>

2

(green- house effect). This temperature change is probably somewhat under- estimated, at least for the future conditions, since the direct radiative effect of N

2

0 , C H

4

and C F C s is not yet included in the model. It is generally assumed (WMO, 1983) that the effect of a doubling of these gases could be as large as the contribution of a doubling in CO

2 >

The model also indicates that the present temperature should be 0.7 K above its preindustrial value. Such a number is difficult to compare with observed data since the "random" perturbations due to volcanic activity which probably lead to a cooling of the Earth's surface (see Brasseur and Solomon, 1984 for a discussion) are not included in the model although the corresponding effects might be larger than the present CC>2 effects.

Total ozone, as shown in table 1, varies by a few percent only and the depletion is never larger than 1 percent. In fact, as indicated by figures 5a and b, the small change in the column results from the difference between a significant ozone depletion in the strato- sphere and a rather similar increase in the troposphere. An examination of fig. 5a shows that ozone is rather stable in the 20-30 km region.

The largest relative depletion at 40 km is due to the action of C F C s . The resulting ozone reduction in the upper stratosphere increases with time until year 2020. After this time, the enhancement in the methane concentration reduces the amount of the active CI (CI and CIO) in favor of the inactive reservoir HCI by reaction

CI + CH, -» HCI + CH„

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T A B L E 1.- Changes in the ozone column A0

3

/C>

3

and in the temperature at the Earth's surface (AT ) as a function of time.

Year

A C

V

0

3 (percent) AT

g

(K)

1950 + 0.5 + 0.2 1983 + 0 . 1 + 0.7 1990 - l.O + 0.8 2000 - 1.0 + 1.0

2020 - 0.6 + 1 . 3

2040 0.0 +1.6

2060 +1.0 +2.0

2080 +3.0 + 2.3

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50

JC E

ÜJ O 30 -

20 -

10 -

OZONE

COUPLED PERTURBATIONS Northern Hemisphere

2080

-20 0 20 AO 60 80 RELATIVE VARIATION (percent)

Relative variation in the ozone concentration with regard to its preindustrial value, corresponding to the adopted perturbations scenario.

50

AO

£ 30 -X

iLl Û 20

ZD

10

"I I r OZONE

COUPLED PERTURBATIONS Northern Hemisphere

- 2

-1 0

ABSOLUTE VARIATION IN CONCENTRATION (lO^cm

3

)

Fig. 5b.- Calculated deviation of the ozone concentration from its preindustrial value, corresponding to the adopted

perturbations of fig. 1-4.

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The ratio CIO/HCI decreases and the efficiency of the destruction of ozone by CI is considerably reduced. As discussed

A

below, the, simultaneous increase in carbon dioxide also lessens the ozone depletion.

The reduction of C>

3

in the lower stratosphere ( r e l a t i v e l y small but rather significant in absolute value) is due to the increase in the N

2

0 and in the associated NO

x

amount. This p e r t u r b a t i o n is small due to the relatively slow prescribed increase in the N

2

0 concentration.

Moreover, the dramatic enhancement in methane leads to a larger OH concentration and consequently a lower N 0

2

/ H N 0

3

ratio. This effect stabilizes ozone in the middle stratosphere.

The rather fast increase in tropospheric ozone which almost counterbalances the decrease in the stratosphere is due, f o r the period p r i o r to 2000, to the rapidly v a r y i n g a i r c r a f t emission. A f t e r year 2000 the NO injection is assumed to remain constant and the slower increase

A

has to be a t t r i b u t e d to the enhancement in the methane concentration.

Sensitivity calculations show that the magnitude of the methane effect on ozone depends much on the amount of NO present in the troposphere. It is therefore required to better understand the absolute values of the tropospheric production rates of NO by l i g h t n i n g , decomposition of PAN, oxidation of NH^ or any other process. In the present model s t u d y , we have adopted a constant

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production of 1000 cm s below 10 km, corresponding to a world c

production of 10 Tons N / y r .

Carbon dioxide has no direct chemical effect below 70-80 km.

It has however a radiative influence and its predicted upward t r e n d should progressively cool the upper stratosphere. Because of the chemical/thermal interaction, a given decrease in the stratopause temperature should increase the local ozone concentration.

Consequently, the adopted scenario for the C 0

2

evolution should

stabilize ozone against the CFC p e r t u r b a t i o n .

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The preceeding results refer to simultaneous effects of various emissions. The response of the atmosphere to individual perturbations has also been considered. When, for example, only a continous injection of CFCs is considered (fig. 1), the ozone amount decreases gradually and the corresponding depletion reaches 3 percent in year 2080. This value does not yet correspond to a steady state. A doubling of nitrous oxide reduces the ozone column by 8 percent and a doubling of methane by about 2 percent. When the amount of carbon dioxide is doubled, the ozone column is increased by 3 percent and the local 0

3

concentration at 40 km is enhanced by about 23 percent.

The temperature in the stratosphere is very sensitive to the chemical composition and especially to the vertical distribution of ozone and carbon dioxide. Both the reduction of 0

3

(due essentially to large C l

x

amounts) and the enhancement of CO^ lead to a decrease in the temperature. Contrary to what happens for the ozone concentration, the simultaneous introduction of the two perturbation's does not stabilize the temperature but leads to a larger cooling. As shown by figure 6, a reduction of more than 20 K should be expected at the stratopause. The modification in the vertical temperature gradient will infer changes in the general circulation patterns. These dynamical effects require, for their study, multidimensional investigations.

CONCLUSIONS

Model calculations show that the injection of several gases released by man-made activity could significantly modify the ozone concentration and the temperature in the stratosphere. These changes should therefore lead to modifications in the strength of the atmospheric dynamics and in the surface temperature. The problem discussed in this paper, because of its climatic implications, requires much attention from the scientific community as well as from the decision makers.

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2 0 TEMPERATURE

COUPLED PERTURBATIONS

-30 -25 -20 -15 -10 -5

TEMPERATURE CHANGE (K)

Fig. 6.- Calculated change in thé temperature from the preindustrial

era, for several years running from the present day to year

2080, corresponding to the scenario described in figures 1-4.

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It should be emphasized t h a t t h e v a r i a t i o n s calculated in t h e model discussed above r e s u l t s from a number of n o n - l i n e a r i n t e r a c t i v e processes w h i c h are not yet completely u n d e r s t o o d . For example, numerical simulations ( P r a t h e r et al, 1984) i n d i c a t e t h a t above a c e r t a i n amount of CI , t h e s e n s i t i v i t y of ozone to odd c h l o r i n e increases

A

s u d d e n l y , leading r a p i d l y to a large ozone d e p l e t i o n s . T h i s n o n - l i n e a r e f f e c t between 0-, and CI is c o n t r o l e d b y odd n i t r o g e n : at h i g h

O A

c h l o r i n e , t h e removal of ozone is dominated b y reactions i n v o l v i n g CIO w h i l e , at low c h l o r i n e , i t is r e g u l a t e d b y reactions w i t h NC^. Detailed analyses are r e q u i r e d to s t u d y such coupled processes w i t h t h e i r implications on the f u t u r e climate.

ACKNOWLEDGEMENTS

I wish to t h a n k A . De Rudder and C h r . T r i c o t f o r several p r o f i t a b l e discussions and help in the computation w o r k . T h i s w o r k was s u p p o r t e d b y t h e Chemical M a n u f a c t u r e r s Association ( C M A ) .

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2

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